Hello all!
I have a question regarding how sequence abstraction works in TR. In the
sequence part of the docs it says that a sequence can consist of lists or
vectors among other things. But does this make a function which ideally accepts
a (Listof a) to accept something that is declared as a (Sequenceof a)? For
example, in TR this works:
(: x (Sequenceof Symbol))
(define x '(a b c d))
However, this shows a type mismatch:
#lang typed/racket
(: step (All (a)
(-> (-> a (Sequenceof a) (Sequenceof a))
a
(Sequenceof a)
(Sequenceof a))))
(define (step fn x seq)
(fn x seq))
(step (ann cons (-> Symbol (Listof Symbol) (Listof Symbol)))
'a
'(b c))
Results in:
Type Checker: Polymorphic function `step' could not be applied to arguments:
Argument 1:
Expected: (-> a (Sequenceof a) (Sequenceof a))
Given: (-> Symbol (Listof Symbol) (Listof Symbol))
Argument 2:
Expected: a
Given: 'a
Argument 3:
Expected: (Sequenceof a)
Given: (List 'b 'c)
I think, trying to instantiate the polymorphic step function might help but I
was not able to figure out how.
Thanks in advance.
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